This invention relates to a circumference measuring gauge of the type which employs a tape curved over an intermediate portion into a closed loop with its two end portions extending away from the loop in opposite directions, two mounting members one fixed relative to each end portion of the tape and mounted for relative movement towards and away from one another to increase or decrease the loop circumference, and means responsive to the distance apart of two datum points one fixed relative to each mounting member to indicate the size of the loop.
U.S. Pat No. 3,967,383 describes such measuring gauges and their operation, and also illustrates the cassette form in which the tape is preferably provided, with its said end portions firmly affixed to respective separate plates which have inwardly directed end portions extending arcuately towards one another around the portion of the circumference of the loop. A particular embodiment of this prior patent comprises in combination a tape including an intermediate portion forming means defining a closed loop with its two end portions extending away from the loop in opposite directions, two mounting members, one fixed relative to each end portion of said tape and mounted for relative movement towards and away from one another in increase or decrease the loop circumference, and means responsive to the distance apart of two datum points, one fixed relative to each mounting member to indicate the size of said loop, means resiliently biasing said mounting members away from each other to tighten said loop, cam means comprising a generally annular body having an inner peripheral cam surface, cam follower means including at least one cam follower member attached to a movable mounting member and operatively engaging said cam surface, said cam means being rotatable and said cam surface having first portions which, when engaged by said cam follower means, moves said mounting members towards each other against said resilient bias to loosen said loop for acceptance or release of a rod to be measured, and second portions which permit said resilient bias to move said mounting members away from each other to tighten said loop around a rod to be measured, motor means operatively associated with said cam means to rotate said cam means, and control means for actuating and deactuating said motor means for rotating and stopping rotation of said cam means, said control means including means for actuating said motor means to rotate said cam means to a first position in which said cam follower means engage said first portions of said cam surface and said loop is at its maximum circumference, means to deactuate said motor means in said first position to permit insertion of a rod to be measured into said loop, means to again actuate said motor means after the rod to be measured is inserted into said loop to rotate said cam means to a second position in which said cam follower means is juxtaposed to said second portions of said cam surface to permit said resilient bias to tighten said loop around the rod to be measured, means to deactuate said motor means in said second position to allow measurement, and means to again actuate said motor means to rotate said cam means to a third position in which the loop is loosened, means to deactuate said motor means in said third position to permit removal from said loop of the rod that has been measured, said means for actuating said motor means to rotate said cam means to said first position being activated on removal of the rod that has been measured from said loop.